Near‐Infrared Laser Light Driven La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag Upconverting Composite Phosphor for Improved Luminescence, Surface Enhanced Raman Spectroscopy, Photocatalytic, and Electrochemical Performance

La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag upconverting composite is a functional phosphor that has been prepared and characterized using techniques such as XRD, FTIR, FESEM, EDX, elemental mapping, Raman spectroscopy, GC–MS, UV–vis, fluorescence microscopy, and electrochemical performance analysis. A comparative study shows that Ag ion incorporation improved the optical SERS response, photocatalytic, electrochemical, and upconversion‐based functional properties. Ag enhances the overall green and red upconversion emission bands of Er 3+ ions by ~3.2 and ~2.7 fold, respectively, in the La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag upconverting composite. The SERS enhancement factor of about ~5.71 × 10 2 has been obtained using RhB probe molecule (Raman mode of ~1660 cm −1 ) by using the La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag upconverting composite‐based substrate under 532 nm laser excitation. Also, the La‐O Raman mode in the La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag reflects a smaller phonon lifetime (1.0 × 10 −13 s) and stronger electron phonon coupling effect as compared to La 2 O 3 :Er 3+ –Yb 3+ . Moreover, near‐infrared (NIR) laser light‐triggered photocatalytic activity of La 2 O 3 :Er 3+ –Yb 3+ and La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag with ~1.22% and ~36.16% degradation efficiency, respectively, has been observed by measuring the degradation of RhB dye after 30 min of 980 nm continuous‐wave (CW) laser irradiation. The study reported here shows that the developed La 2 O 3 :Er 3+ –Yb 3+ @SiO 2 /Ag upconverting composite exhibits functional properties for a variety of applications, including upconversion, SERS substrate‐based Raman enhancement, and NIR‐driven photocatalytic degradation.